2024 AIChE Annual Meeting
Quantifying Oxidation of Hafnium, Niobium, Tantalum, and Zirconium High Entropy Alloy
Newer generation heat engines and exchangers – such as hydrogen internal combustion engines – achieve high efficiencies because of the high temperatures that are reached inside of the combustion chambers. These temperatures can reach as high as 1500 °C, which many current steels and alloys cannot withstand. As temperatures and efficiencies continue to rise, new materials are needed to be developed that are able to withstand these high temperatures. High entropy alloys (HEAs) are a class of materials composed of 4 or more elements mixed in nearly equiatomic compositions and have shown the potential for improved material performance in high temperature, corrosive, and irradiation environments. This work explores the oxidation and irradiation performance of a HfNbTaZr. Isochronal annealing at 600, 700, 800, and 900 °C coupled with mass change measurements enable calculation of the oxide growth rate, while in-situ Thermogravimetric Analysis (TGA) and in-situ X-ray Diffraction (XRD) up to 900 °C decipher the real-time phase and oxide growth changes. Post-exposure analysis with XRD and SEM offer information on the development of new phases and the spatial distribution of oxide formation. XRD analysis provided valuable information about the likelihood of each element oxidizing, with Ta and Zr being much more likely to oxidize as compared to their Hf and Nb counterparts. This was in contrast to the in-situ SEM annealing experiments, highlighting the differences between testing techniques. Finally, initial results on the irradiation stability of the HfNbTaZr HEA under 2.8 MeV Au ion irradiation offers insights on the performance of this HEA composition in multiple extreme environment conditions. This work can inform future alloy design to develop optimized HEAs and materials to better withstand higher temperatures, which is a key cornerstone to next generation Carnot heat engines – and the next step towards a zero-emission world.